Matrix's federation already does result in redundancy of the entire chat history; users not on @matrix.org can currently communicate between each other just fine even on :matrix.org rooms despite matrix.org being down.

It's entirely just user accounts that are tied to a homeserver currently. There's a proposal to make it possible for clients to fully manage their account identity (https://github.com/matrix-org/matrix-spec-proposals/pull/408...) but that doesn't look particularly active.